Many semiconductor manufacturing processes involve the use of a gas distribution system that distributes process gases across the surface of a semiconductor wafer during semiconductor processing operations using a “showerhead.” The showerhead is typically the same diameter, or a slightly larger diameter, as the wafer being processed and includes one or more internal plenums and a large number of small ports that are located on the side of the showerhead facing the wafer and that lead to the internal plenum. Gas that is introduced into the internal plenums of the showerhead flows out of the internal plenums via the small ports and is thus distributed across the semiconductor wafer. The gas is typically introduced to the showerhead's internal plenums by a stem tube that is connected to one or more process gas sources.